A surgically created systemic arterial-to-pulmonary arterial shunt currently is used in the palliation of the hypoxic infant with congenital cyanotic heart disease. Assessment of patency and function of these shunts created to augment pulmonary blood flow remains a significant clinical problem. Intraoperatively, shunt adequacy is determined by evaluation of transient measurements such as changes in diastolic blood pressure, mean blood pressure, heart rate and arterial pO2 level as the shunt is manipulated. This study will evaluate the effectiveness of transcutaneous pulsed Doppler ultrasound (PDU) carotid arterial blood velocity measurements as a method for determining the adequacy of surgically created shunts both intraoperatively and postoperatively. An 8 MHz pulsed Doppler velocimeter will be used to measure carotid arterial blood velocity preoperatively, intraoperatively as the shunt is manipulated from open to closed by the surgeon, and immediately, 24, 48, and 72 hours postoperatively. Three indices--1) the ratio of integrated diastolic velocity to integrated systolic velocity (DV/SV), 2) the ratio of the end diastolic velocity to the peak systolic velocity (EDV/PSV), and 3) the ratio of reverse velocity to forward velocity (R/F)-- are derived from the recorded velocity tracings of at least 5 consecutive cardiac cycles to quantitatively describe the waveform. To categorize shunt function intraoperatively the difference between the means of each index for the shunt open state and the shunt closed state will be compared with shunt efficacy during the immediate postoperative period. This will establish a range of values for which the shunt is optimal while the patient is still in surgery. Postoperative velocity indices will be compared with the concurrent clinical status of shunt functions as well as 2 measurements of Qp/Qs, as determined by radionuclide angiocardiography. These comparisons will establish a range for each index in which the shunt is functioning properly during the postoperative period. Additionally, to determine whether Doppler derived indices are affected by changing hemodynamic parameters other than shunt flow, a canine model of shunt flow will be employed. The model will use various hemodynamic altering drugs while comparing shunt flow to the Doppler indices for each drug. Preliminary data suggest that noninvasive PDU velocity waveforms and derived indices correlate well with the magnitude of shunt flow in the acute operative setting. This method is a potentially inexpensive, repeatable, and safe alternative to aortography.